An investigation of two behavioural economic approaches to evaluating reinforcer value

This study compares two approaches for comparing the value of two different reinforcers. The own-price demand method compares the changes in consumption of the reinforcers resulting from increases in the number of responses required to gain access to the reinforcers. Experiment 1 assessed own-price demand for two reinforcers. Six hens responded under increasing fixed-ratio schedules when either wheat or puffed wheat was delivered for key-pecking. The quantity consumed (measured as either numbers of reinforcers obtained or weight of food consumed) was plotted against the FR size on log-log coordinates to give the own-price demand functions. Three functions were fitted to the data and all described the data well. The parameter values from Hursh’s (1988) and Hursh and Winger’s (1995) equations were generally consistent with wheat being the preferred reinforcer data when derived from the weight of food consumed. Those derived from number of reinforcers were inconsistent. The essential value, α, from the equation proposed by Hursh and Silberberg (2008), when k was fixed at 6.5, were smaller when weight was used and were weight was used and were larger when number of reinforcers was used as the consumption measures and so suggested the essential value changed. These data show that the outcome is affected by how the consumption is measured. It seems that that the above models were similar. The cross-price demand method examines the divergence of the cross-point of two demand functions. In Experiment 2 assessed the cross-point using the same six hens responding under concurrent fixed-ratio fixed-ratio schedules over nine pairs of schedules: FR1/FR256, FR8/FR32, FR128/FR2, FR4/FR64, FR256/FR1, FR32/FR8, FR2/FR128, FR16/FR16 and FR64/FR4. In Condition 1 both schedules gave access to wheat, in Condition 2 both gave puffed wheat, and in Condition 3 one gave wheat and the other puffed wheat. The numbers of each reinforcer obtained and weight of each food consumed were plotted as functions of the left fixed-ratio values to give the cross-price demand functions. When the two reinforcers were identical the cross point tended to be around the ratio used for the equal schedules session (16) with both number of reinforcers and weight of food.. When the two reinforcers differed the cross point for most hens moved to higher ratio when weight of food consumed was used, suggesting that wheat was more valued than puffed wheat for these hens. This was not so for number of reinforcers. Both experiments show that how the consumption was assessed affected the conclusions from that method. Overall the cross-price demand analysis appeared to be the easier to interpret